One such mobile communication platform, India-headquartered Nimbuzz, around since 2007, is now revving up its game in hopes to increase its users from 150 million to 1 billion soon.

Its VoIP voice calling feature – the only IM player in India to legally offer it since inception -- is already a one-up to WhatsApp, which is now planning to introduce voice calling after Facebook's acquisition.

Shahnawaz Karim, head of marketing for Nimbuzz, said, "Until now, our focus was to ensure all our verticals like messaging, chat, video and voice calling were in place. However, now our focus is on increasing voice calling capability by enabling our chat users to migrate to voice calling."

The VoIP voice calling also gives Nimbuzz an upper hand amongst its peers, Wechat, LINE, and Facebook messenger, as well as telecom operators – given that Nimbuzz's international call rates are much cheaper than most telcos.

"When we started offering international calls over VoIP, however, we offered calls to US and Europe for as low as 60 paise a minute, at a time when telcos were offering rates of Rs 8 per minute. Last year, however, our tie-up with Spectranet enabled international calls to the US for as little as 1 paisa per second – which has only recently become on par with a few telcos that have slashed international tariffs by 80-90%. However, we expect our charges to decrease even further with lower termination costs," said Karim.

To solve the problem of voice calling quality in India, Nimbuzz has its own compression engines which ensure calls are compressed with data, making sure that you can even terminate a plan with Edge network. Plus, Nimbuzz's VoIP allows a call even if only one party is on data and the other partner is not.

Nimbuzz, which has 150 million users globally and 25 million in India, growing at the rate of 210,000 users on a daily basis – or almost 1 user per second, as recently as last week emerged with a new look – syncing its interface with the operating system of its individual user, instead of the earlier standard Nimbuzz interface.

However, Nimbuzz management insists it's not in for the numbers game, but is rather focused on increasing usage and engagement of its existing users.

Tanay Chaturvedi, assistant manager – marketing (global) for Nimbuzz, said, "While most of the IM players in the market now are busy acquiring users, our focus on acquisitions was probably two years ago.

We believe with growing mobile data usage there will come a time of saturation, and so we believe it is more important to retain users and keep them engaged. Besides, Nimbuzz users are slightly different from pure-play SMS replacement users – they spend larger amounts of time on Nimbuzz apart from chat and voice calling, for features such as chatrooms, videos, virtual gifts – all of which are increasingly gaining popularity."

Nimbuzz chatrooms – which saw a 30% spike in usage after the exit of Yahoo! Chatrooms from the space – is especially popular amongst Nimbuzz's 40-50 million Middle East users- its second largest focus market after India.

Karim said, "At any given time, we have 50,000 chatrooms active at any point in time, and we probably have more than 1 million users coming on a particular chatroom per day – with 25 users in one chatroom at one go. Some users even pay to get their chatroom registered as 'popular' on Nimbuzz."

And while Nimbuzz will not compromise its users' privacy by allowing their contacts database to be accessed the way WhatsApp has, it is confident of getting users thanks to its free service, and also thanks to the fact that it has partnerships with all telcos that add to the stickiness factor, while increasing telcos' Arpus. A good example is Mobilink – Pakistan's number one telco which saw its data usage double after partnering with Nimbuzz and has now extended Nimbuzz's contract from three months to a year.

That said, Nimbuzz, which is close to break-even, derives 20-30% of revenues from voice calling, 10% from virtual gifts and 60-65% is from mobile advertising.

And what is the plan ahead for India?

"While everything is tested and built from India, we are present in eight Indian languages – which includes local language interface. This is out of the 42 global languages capability we offer. We also work very closely with Nokia for Windows, and have partnered for Nokia X, as well. Apart from that, we do a lot of innovation for India and Middle East, and while in India we are on par with Whatsapp, in the Middle East we are bigger than Facebook Messenger on mobile," Chaturvedi said.

Going forward, video calling would be the next big thing after voice calling for Nimbuzz.

"While we have video chatting and hand-picked videos for our users in place, we are working closely with telcos for improved video calling functionality which we think will catch up in a big way in the next two years with better bandwidth, when users go from chat to calling and calling to video," said Karim.